In a conventional compressor mounted on, for example, a vehicle, in order to seal a periphery of a rotational shaft protruding from its housing outwardly, a lip-type seal is fitted between the housing and the rotational shaft so as to isolate an internal space (fluid) F in the housing from atmosphere A.
An example of such a known lip-type seal is shown in FIG. 1. This lip-type seal is made up of a seal ring 1 and a support ring 2. The seal ring 1 is made of an elastic material like rubber so as to define a fitted part 1a fitted to a hole Ha of a housing H, and a lip part 1b conically extending from the fitted part la inwardly in a radial direction. The support ring 2 includes a joint part 2a joined to the fitted part la and a supporting part 2b that extends from the joint part 2a to a middle of the lip part 1b and that supports the lip part 1b from inside (see Japanese Patent No. 3346743, for example).
In this lip-type seal, the lip part 1b of the seal ring 1 is supported by the supporting part 2b of the support ring 2 from inside, and, in order to improve rigidity of the lip part 1b, the lip part 1b is formed to have substantially the same thickness from its root side to its end.
Additionally, even when pressure applied by a fluid F is high, the end of the lip part 1b is kept in line contact with an outer peripheral surface of a rotational shaft S by controlling the lip part 1b so that the lip part 1b can hardly be deformed.
However, if CO2 or the like is used as a refrigerant of the compressor, the seal is placed in a high-pressure environment of at least 5 MPa in regular use. Therefore, a conventional problem resides in that the lip part 1b is increasingly worn out, and durability is lowered in spite of the fact that the lip part 1b is supported by the support ring 2.
The present invention has been made in consideration of this problem of this conventional seal, and it is an object of the present invention to provide a lip-type seal capable of securing sealability in a high-pressure environment and having excellent durability in a simple structure.